This invention relates to the field of telecommunication and more specifically to an xDSL repeater system and method.
As demand for broadband services, such as high speed Internet access and on-demand video to the home increases, the need for technologies that can transmit large bandwidths of information also increases.
One technology being introduced to fill this need is digital subscriber lines (xDSL). The advantage of xDSL over other broadband technologies such as fiber optics to the home or cable modems is that it uses the existing twisted pair copper lines that already provide telephone services to homes.
The term xDSL is a catchall term covering a number of similar technologies. These include High bit rate Digital Subscriber Line (HDSL) and Asymmetric Digital Subscriber Line (ADSL).
HDSL is designed to deliver T1 (1.544 Mbps) and E1 (2.048 Mbps) services over conventional copper lines by using transceivers on each end of two or three twisted pairs. Single pair HDSL is limited to 384 Kbps or 768 Kbps symmetrical speeds.
ADSL uses conventional twisted pair copper lines to provide a large downstream path and a smaller upstream path. This allows for services such as on demand video and high speed Internet access where the user needs to receive greater bandwidth than the user needs to send. In one embodiment, ADSL is capable of providing downstream rates in excess of 6 Mbps and simultaneous duplex transmissions of 640 Kbps. Several competing ADSL standards exist. These include Discrete Multitone (DMT) and Carrierless Amplitude and Phase modulation (CAP). In one embodiment, DMT divides the 1 MHZ phone line spectrum into 256 4 KHz channels. Transmission bit density can be varied to overcome noise and interference.
CAP uses a single carrier and utilizes amplitude modulation similar to that used for modems to achieve ADSL transmission.
Both DMT and CAP operate by placing an ADSL modem on either end of a twisted-pair telephone line (one at a central office and the other at the customer""s home or office). Three channels are created: a POTS (plain old telephone service) channel, a medium speed duplex channel and a high speed downstream channel. In a typical embodiment, POTS takes up the first 4 KHz of the phone line spectrum. The medium speed duplex channel and the high speed downstream channel occupy higher frequencies in the spectrum. Since the POTS channel is located in the first 4 KHz of the spectrum it can be split off from the data channels by filtering, thus providing an uninterrupted POTS connection.
One drawback of xDSL systems is that transmission signals attenuate as line length increases. For example, in order to maintain a downstream rate of around 6 Mbps the maximum loop length of copper is 12,000 Feet. This drawback limits the number of homes that can access xDSL service.
Accordingly, a need has arisen for an xDSL Repeater System and Method. The present invention includes a system and method that provides a xDSL repeater that addresses the shortcoming of prior systems and methods.
According to one embodiment of the invention, a system for repeating an xDSL signal is provided. The system is comprised of two receiver/transmitters. The receivers consists of an analog front end which amplifies and converts the analog signal to the digital domain. The digital data is passed to a digital signal processor which is responsible for time and frequency domain equalization, echo cancellation, and decoding the signal. The transmitters take the decoded data and encode the data, transfer it to the analog front end where it is converted to an analog signal, amplified, and sent down the remainder of the cable to the far end transceiver. Also, a replica of the transmitted signal is transferred to the receiver DSP to remove crosstalk that is induced on the line when the powerful transmitted signal leaves the repeater adjacent to the weaker received signal.